How does the NSI2000 software calculate the S/N signal-to-noise value in the real-time monitor display?
The real-time S/N level is determined by monitoring the amplitude variation over time and then computing the corresponding Error/Signal (E/S) level required to cause that level of amplitude variation. The noise is treated as an error relative to a peak, or perfect, signal and may be represented in one of two ways: either as an uncertainty in amplitude or as an error below the signal peak. As shown in the plot below, a small variation in amplitude, or uncertainty, results in an exponential change in the E/S level, or S/N. The S/N value in the NSI 2000 real-time monitor is a convenient method of conveying the actual noise level, relative to the signal, currently present in the measurement. The table shows the uncertainty for various S/N levels. Note that the a 20 dB improvement in S/N reduces the uncertainty by factor of 10. The exponential nature of the relationship is shown in the plot.
